I disagree. Complex scripts end up having wonky naming conventions and odd dependencies as procedural code gets longer and longer. I'd much rather see code grouped together in classes. Its clearer when code is grouped together, easier to see the purpose, and can help reduce the spaghetti I so often see... IMO at least.
OK. I'd stick with procedural, but if you want OO there are plenty of options, your best choice would depend on how OO intensive your use of OO would be. If you want to use a lot of OO features (inheritance, etc) then a Tcl extension would be your best bet. You should be able to find something suitable even for Tcl8.4, which I think is still used in some EDA tools, even though 8.4 it's no longer developed :). At the other extreme, if you were just thinking of classes for scoping variables and procedures, but aren't going to be creating more than one object of a "type", then consider using namespaces instead. Another alternative, somewhere in the middle ground, if you wanted a class for scoping and for creating multiple objects of a "type", without heavy use of other OO techniques, then you don't need a Tcl extension for that, you can do that with about half a page of code. Dare I say it, you should be able to find all that stuff on the Tclers Wiki :)